1. Field of the Invention
The present invention relates to a method for manufacturing a filler neck for feeding fuel into a feeding pipe of a motor vehicle or the like.
2. Description of the Related Art
From the viewpoint of efficiency in feeding fuel, reduction of manufacturing cost, or reduction of weight of the product, a pipe having a smaller diameter relative to the conventional pipe is often employed as a feeding pipe, recently. However, the legal regulations require a mouthpiece of the filler neck to have the diameter as large as that of the conventional one, so that it tends to become a larger diameter of the mouthpiece relative to that of the feeding pipe. In a case of a feeding pipe having a large diameter, it can be used as the filler neck as it is enlarged diameter of edge portion of the feeding pipe. To the contrary, a feeding pipe having a smaller diameter requires an additional step to joint a mouthpiece manufactured separately to the feeding pipe to form a filler neck. (JP-A-H09-066747, JP-B-H06-020824, JP-U-H06-012987, U.S. Pat. No. 6,330,893, U.S. Pat. No. 6,588,459, etc.)
Specifically, the conventional filler necks are formed by fitting a circumferential wall portion of the mouthpiece in the feeding pipe, and by jointing the overlapped circumferential wall portions. The conventional jointing methods are exemplified by MAG welding, TIG welding and brazing. In general, the joint portion between the mouthpiece and the feeding pipe requires sufficient hermeticity. Thus, a presence of clearance for filling sub-welding materials or for brazing is required between the mouthpiece and the feeding pipe. That is, conventional joint methods require an additional procedure for filling the clearance between the mouthpiece and the feeding pipe so as to be completely sealed after the junction process.
In addition, by the MAG welding or the TIG welding, it is hard to keep hermeticity of the joint portion because of burning through a peripheral edge of the feeding pipe. These welding methods also cause inevitable scattering of the welding spatters which cause danger in the welding environment. Moreover, both the methods increase manufacturing costs of the process of forming the joint between a mouthpiece and a feeding pipe due to applying sub-materials for and welding at low-speed. In a case of manufacturing a filler neck in a variety of sizes in small runs, variation in the size of a mouthpiece and a feeding pipe causes the quality of welding finishing of the products to be unstable. As a result, a joint strength and hermeticity of the products becomes unstable.
As for brazing, a condition of the clearance to obtain the products with sufficient welding strength and hermeticity becomes more difficult than that of the aforementioned welding methods. Generally, the brazing provides a relatively high joint strength with the clearance sized in a range of 3/100 mm through 1/100 mm. However, the joint strength significantly drops with the clearance of 1/100 mm or less. Thus, the size management of the clearance is more delicate in brazing than in welding. Moreover, the brazing with silver-solder, for example, might bring deterioration to work environment due to generation of fluorine compounds or boron compounds during brazing.
Thus, in the conventional methods for manufacturing a filler neck by utilizing MAG welding, TIG welding or brazing, there have been existing problems of fuel evaporation due to insufficient hermeticity of a filler neck, or of low productivity. In response to the recent requests for solving these problems, the present inventors have conducted investigations to find a method for manufacturing a filler neck to joint a mouthpiece and a feeding pipe which were separately manufactured as individual members.